Chemiluminescent reactions of lead with N 2O, O, O 2, and O 3 have been investigated by studying the spectrum of PbO under a wide variety of reaction conditions. Spectra were found to be very dependent on the oxidant used and the pressure. It was found that addition of active nitrogen greatly increased the PbO emission and also produced strong atomic Pb lines. Many new bands of PbO have been observed and measured in the A0 +- X0 + and a1- X0 + systems leading to the following molecular constants. AO +: T e = 19862.6 ± 3.0 cm-1; ω e = 444.3 ± 1.6 cm-1; ω eχ e = 0.54 ± 1.4 cm-1a1: T e = 16024.9 ± 2.9 cm-1; ω e = 481.5 ± 1.4 cm-1; ω eχ e = 2.45 ± 1.44 cm-1XO +: ω e = 720.97 ± 0.72 cm-1; ω eχ e = 3.536 ± 0.050 cm-1 An approximate value of B = 0.252 ± 0.010 cm -1 was obtained for the a state.